1. Field of the Invention
The present invention relates to a method for copying by an image forming apparatus such as a copying machine capable of making a duplex copy in a manner that in a first circulation of documents fed from document feeding means, sheets onto whose one side an image of one of even or odd ordinal numbered documents is transferred (referred to one-side-transferred sheets hereinafter) are stored in an intermediate tray, and in a second circulation of the documents, the one-side-transferred sheets stored in the intermediate tray are fed to image transferring means to transfer an image of the other pages of the documents onto the other side of the one-side-transferred sheets.
2. Description of the Related Art
With reference to a method for copying by a conventional copying machine, it is known that an intermediate tray of the copying machine comprises a cycle detecting sensor and a cycle detecting lever, wherein the lever is provided with the sensor and, in a mode that two sets of copy of the documents are temporarily stocked in the intermediate tray, for example, in S.fwdarw.D mode (one-sided documents to double-sided copy), used for separating each set.
In the prior art, when it is judged that the cycle detecting sensor is out of order, an operation of copying in S.fwdarw.D mode is disabled and a double-sided copy cannot be obtained.
Even when the cycle detecting sensor is out of order, a duplex copy can be made, with the result that the user does not notice that a breakdown has occurred and hence the breakdown remains without being fixed. In the case where an operation of copying in S.fwdarw.D mode is continued without the breakdown being fixed, a drum is caused to rotate in skip mode about two times as many as the case of non-skip mode, so that a problem will arise such that the drum cannot last for the specified life time.
In a state that a sensor for detecting the presence or absence of sheets in the intermediate tray does not detect the presence of sheets and the cycle detecting sensor of the intermediate tray is off, when a copying operation is started, the copying machine stops operating due to a misdetection of the sensor.
In the prior art, when it is judged that the cycle detecting sensor is out of order, an operation of copying in D.fwdarw.D mode (double-sided documents to double-sided copy) is disabled and a double-sided copy cannot be obtained.